This invention relates in general to orthopedic surgical implants and, more specifically, to a polymer- or hybrid-based metal/polymer pedicle screw fixation system for use in the field of surgical spine treatment.
Surgical techniques for the treatment of spinal injuries or deformities are usually aimed at joining together two or more vertebrae of the spine, through a process that is called spinal fusion. A spinal fusion technique relies on a fixation system that is anchored to the spine by way of orthopedic screws. These screws are implanted into the pedicles of two or more subsequent vertebrae. The screws implanted into each pedicle are connected together by means of rigid or semi-rigid rods. These rods engage a transverse hole provided in the screw heads, for example, as shown in FIG. 1.
Spinal fixation can be used to treat scoliosis, spondylolisthesis, degenerative disc disease, vertebra fracture, and other spinal disorders or abnormalities. These screws provide rigidity to spinal segments by mechanically immobilizing them. Spinal fixation devices are also used to correct abnormal curvature of the spine.
Pedicles connect the vertebral body to the posterior elements. Each vertebra has two pedicles. Pedicle screws include a threaded shaft and slots at the screw head. The threaded shafts are screwed into the spine through the respective pedicles and a rod locks the screws in place to minimize relative motion, often resulting in a loosening of the screws. The rods are typically locked into place with a fastening screw or set screw.
Current pedicle screws are made out of metal, typically, stainless steel or titanium. These metal screws are very rigid. This high level of rigidity has shown to cause screw loosening in elderly patients or patients with soft bone, as in the case of osteoporosis, multiple myeloma or tumor. These problems include screw loosening, adjacent level degeneration and facet joint degeneration.
There is a continuing need for a pedicle screw fixation system that militates against screw loosening in use. Desirably, the pedicle screw fixation system also militates against adjacent level degeneration and facet joint degeneration.